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https://issues.apache.org/jira/browse/DERBY-6940?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Harshvardhan Gupta updated DERBY-6940:
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Description:
Derby should collect extra statistics during index build time, statistics
refresh time which will help optimizer make more precise selectivity estimates
and chose better execution paths.
We eventually want to utilize the new statistics to make better selectivity
estimates / cost estimates that will help find the best query plan. Currently
Derby keeps two type of stats - the total row count and the number of unique
values.
We are initially extending the stats to include null count, the minimum value
and maximum value associated with each of the columns of an index. This would
be useful in selectivity estimates for operators such as [ IS NULL, <, <=, >,
>= ] , all of which currently rely on hardwired selectivity estimates.
was:Derby should collect extra statistics during index build time, statistics
refresh time which will help optimizer make more precise selectivity estimates
and chose better execution paths.
> Enhance derby statistics for more accurate selectivity estimates.
> -----------------------------------------------------------------
>
> Key: DERBY-6940
> URL: https://issues.apache.org/jira/browse/DERBY-6940
> Project: Derby
> Issue Type: Sub-task
> Components: SQL
> Reporter: Harshvardhan Gupta
> Assignee: Harshvardhan Gupta
> Priority: Minor
> Attachments: DERBY-6940_2.diff, DERBY-6940_3.diff, derby-6940.diff
>
>
> Derby should collect extra statistics during index build time, statistics
> refresh time which will help optimizer make more precise selectivity
> estimates and chose better execution paths.
> We eventually want to utilize the new statistics to make better selectivity
> estimates / cost estimates that will help find the best query plan. Currently
> Derby keeps two type of stats - the total row count and the number of unique
> values.
> We are initially extending the stats to include null count, the minimum value
> and maximum value associated with each of the columns of an index. This would
> be useful in selectivity estimates for operators such as [ IS NULL, <, <=, >,
> >= ] , all of which currently rely on hardwired selectivity estimates.
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